The present invention relates to a spectrophotometer, which can be used by itself, or used as a detecting section in a liquid chromatograph.
FIG. 3 is a schematic view showing a conventional spectrophotometer. A light from a D2 lamp (deuterium discharge tube) 2 as a light source is sent to a mirror 4 via an optical system, not shown, which is formed of a lens, a mirror, a slit and the like. The light reflected by the mirror 4 is sent to a grating 6, and is divided by the grating 6. Then, the light with a specific wavelength is irradiated via a mirror 8 to a flow cell 10 disposed at a detection position. The light from the cell 10 is detected by a photodiode 12 as an optical sensor.
The grating 6 is rotated by a grating driving motor 14 and sends light having different wavelengths to the mirror 8 and the cell 10 in accordance with an angle of the grating 6. Also, there is provided a grating home position sensor 16 for detecting a predetermined position (home position) which becomes a reference at the time of determining the angle of the grating 6.
In the detector as described above, in order to confirm that the light is properly dispersed or provided in accordance with the set wavelengths, when the power is switched on, a position of the grating 6 called an original position, or also called a zero-order light position where a zero-order light or original of the D2 lamp is received on the cell 10, a position of the grating 6 called a 486 nm bright line position where a bright line in a wavelength of 486 nm of the D2 lamp is received, and a position of the grating 6 called a 656 nm bright line position where a bright line in a wavelength of 656 nm is received, are detected to carry out a wavelength check. FIG. 4 is a waveform diagram showing a spectrum of D2 lamp.
In explaining operations at the time of switching on the power supply, after the power supply is switched on, the D2 lamp 2 is lighted up, and the grating 6 is rotated in a direction toward the sensor 16 by the grating driving motor 14. When the sensor 16 responds thereto to become xe2x80x9cOFFxe2x80x9d from xe2x80x9cONxe2x80x9d, the rotation of the grating 6 is stopped, and the grating 6 is located at the home position.
Next, a transmitted light from the cell 10 is detected by the optical sensor 12, and while being monitored, the grating driving motor 14 is driven, so that the grating 6 is rotated step by step from the home position to thereby scan a certain angle range which is determined in advance. Accordingly, a position of the grating 6 where an amount of the light transmitted through the cell is the largest is obtained, and this position is stored as an original position.
Further, based on the original position as a reference, the grating 6 is rotated step by step, to thereby carry out the detection of the 486 nm bright line position and the 656 nm bright line position of the grating 6. From a relational expression, which is determined in advance, between a number of steps of the grating driving motor 14 and the wavelength, a number of steps from the original position corresponding to the 486 nm bright line position and a number of the steps from the origin position corresponding to the 656 nm bright line position are respectively calculated. The number of the steps at the time of detecting the bright line is compared with the number of the steps obtained by the relational expression, so as to carry out the wavelength check.
In case the spectrophotometer shown in FIG. 3 is applied to a detector of the liquid chromatograph, since an absorption of light by a sample generally occurs in the short wavelength region around 210 nm to 300 nm in the liquid chromatograph, the spectrophotometer is used by setting the detected wavelength at the short wavelength region (refer to arrows showing a wavelength region used for detection in FIG. 4).
In the spectrophotometer shown in FIG. 3, the wavelength check is carried out in the wavelength regions (486 nm and 656 nm) which are different from the short wavelength region used for detection. As described above, in case the wavelength region used for the detection differs from the wavelength region used for the wavelength check, the wavelength accuracy is lowered or deteriorated. Thus, it is preferable to carry out the wavelength check in the wavelength region used for detection.
Accordingly, an object of the invention is to provide a spectrophotometer which can carry out a wavelength check in a wavelength region used for detection.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned object, the present invention provides a spectrophotometer which comprises an optical system for irradiating light from a light source to a detection position; a light detecting section for detecting the light from the detection position; a spectral element driving mechanism for changing an angle of a spectral element provided on an optical path between the light source and the detection position or an optical path between the detection position and the light detecting section; and a reference position detecting section for detecting a reference position of the spectral element where a zero-order light or the bright line is irradiated to the detection position based on electric signals from the light detecting section and the dispersing element driving mechanism. As the light source, the spectrophotometer of the invention includes therein a lamp for detection, which is provided for irradiating a light in a wavelength region used for detection, and a lamp for wavelength check, which has a bright line in the wavelength region used for detection.
By detecting the reference position of the spectral element by using the bright line of the lamp for wavelength check within the wavelength region used for detection, the wavelength check in the wavelength region used for detection is carried out. Accordingly, an accuracy of the spectral wavelength can be improved.
Throughout the specification, the reference positions mean an original position at the spectral element where zero-order or original light of the lamp for detection is ejected, and the bright line positions at the spectral element where the bright lines of the lamp for detection and the lamp for wavelength check are respectively ejected.